4,625 research outputs found
Characterization of a Quantum Light Source Based on Spontaneous Parametric Down-Conversion
We have built a quantum light source capable of producing different types of
quantum states. The quantum light source is based on entangled state
preparation in the process of spontaneous parametric down-conversion. The
single-photon detection rate of eight-hundred thousand per second demonstrates
that we have created a bright state-of-the-art quantum light source. As a part
of the characterization we measured two-photon quantum interference in a
Hong-Ou-Mandel interferometer.Comment: 33 page
A multiphase series-resonant converter with a reduced number of thyristors and common grounds for inputs and outputs
Multiphase series-resonant (SR) power converters provide a flexible way to transform power between a utility grid and a multiphase load or source. The current implementations all suffer from a high component count, which makes the use of these converters unattractive from an economical point of view. A new topology for multiphase SR converters has been proposed previously in a simulation context. This topology uses half the number of power semiconductors compared to the existing multiphase SR converters. The present paper addresses the implementation of the new topology in a prototype converter. Simulation data and measured waveforms are shown, and a comparison is made between the new and the existing topologies. It is shown that the economical gain due to the reduction in component count is offset by a lower power ratin
Recommended from our members
Palm phytoliths of mid-elevation Andean forests
Palms are one of the most common tropical plant groups. They are widespread across lowland tropical forests, but many are found in higher altitudes have more constrained environmental ranges. The limited range of these species makes them particularly useful in paleoecological and paleoclimate reconstructions. Palms produce phytoliths, or silica structures, which are found in their vegetative parts (e.g., wood, leaves, etc.). Recent research has shown that several palms in the lowland tropical forests produce phytoliths that are diagnostic to the sub-family or genus-level. Here we characterize Andean palm phytoliths, and determine whether many of these species can also be identified by their silica structures. All of our sampled Andean palm species produced phytoliths, and we were able to characterize several previously unclassified morphotypes. Some species contained unique phytoliths that did not occur in other species, particularly Ceroxylon alpinium, which is indicative of specific climatic conditions. The differences in the morphologies of the Andean species indicate that palm phytolith analysis is particularly useful in paleoecological reconstructions. Future phytolith analyses will allow researchers to track how these palm species with limited environmental ranges have migrated up and down the Andean slopes as a result of past climatic change. The phytolith analyses can track local-scale vegetation dynamics, whereas pollen, which is commonly used in paleoecological reconstructions, reflects regional-scale vegetation change
Bistable hysteresis and resistance switching in hydrogen gold junctions
Current-voltage characteristics of H2-Au molecular junctions exhibit
intriguing steps around a characteristic voltage of 40 mV. Surprisingly, we
find that a hysteresis is connected to these steps with a typical time scale >
10 ms. This time constant scales linearly with the power dissipated in the
junction beyond an ofset power P_s = IV_s. We propose that the hysteresis is
related to vibrational heating of both the molecule in the junction and a set
of surrounding hydrogen molecules. Remarkably, we can engineer our junctions
such that the hysteresis' characteristic time becomes >days. We demonstrate
that reliable switchable devices can be built from such junctions.Comment: Submitted to Phys. Rev. Let
Localized states influence spin transport in epitaxial graphene
We developed a spin transport model for a diffusive channel with coupled
localized states that result in an effective increase of spin precession
frequencies and a reduction of spin relaxation times in the system. We apply
this model to Hanle spin precession measurements obtained on monolayer
epitaxial graphene on SiC(0001) (MLEG). Combined with newly performed
measurements on quasi-free-standing monolayer epitaxial graphene on SiC(0001)
our analysis shows that the different values for the diffusion coefficient
measured in charge and spin transport measurements in MLEG and the high values
for the spin relaxation time can be explained by the influence of localized
states arising from the buffer layer at the interface between the graphene and
the SiC surface.Comment: 6 pages, 3 figures, including supplementary materia
Insecure tenure in Amsterdam:who rents with a temporary lease, and why? A baseline from 2015
Given that insecure leases impact negatively on ontological security and subjective well-being, and given increasing pressure on European housing markets, more insight into insecure leases is timely. In this article, we assess the occurrence of temporary leases in the city of Amsterdam in 2015, and explore the characteristics of the tenants. We employ hitherto underused local survey data (N = 17,803). Although permanent contracts are still dominant, the majority of young adults aged 18–23 are renters with a temporary lease. Students, those with a Western migration background, those who moved because their previous rental contract was terminated or because the previous dwelling was too expensive, and those who moved from abroad were particularly likely to have a temporary lease. Families were unlikely to have a temporary lease. Given recent developments–in 2016 temporary leases were legally established as a regular tenure in the Netherlands–the number of temporary leases may increase sharply from the reported baseline of 2015
Polymer-Encapsulated Halide Perovskite Color Converters
An easy process to fabricate highly luminescent and color-pure polymer-encapsulated halide perovskite color converters is reported. Methylammonium lead bromide (MAPbBr3) with an additive of amantadine hydrochloride is prepared by dry mechanochemical synthesis together with an encapsulating polymer. (In this report, poly(methyl methacrylate), polystyrene, and polyethylene oxide are investigated.) The composite material is heated and pressed into a thin disk exhibiting strong luminescent properties. By adjusting the weight percentage of the perovskite in the polymer, the disk can be opaque or transmissive. The disks are stable in air for over 2 months. By inserting a secondary emitter, white light can be obtained by illuminating it with a blue light source
- …